Electrodeposition of alloys containing copper and tin



United States Patent ELECTRODEPOSITION OF ALLOYS CONTAINING COPPER AND TIN Erich Heymann and Grigory Schmerling, London, England, assignors to Silvercrown Limited, London, England, a British company No Drawing. Application May 17, 1954, Serial No. 430,425

Claims priority, application Great Britain June 4, 1952 6 Claims (Cl. 204-'44) This application is a continuation-in-part of our application, Serial No. 334,088, filed January 29, 1953, now abandoned,

The present invention relates to improvements in electroplating and is more particularly concerned with the electrodeposition of alloys containing copper and tin as the main constituents.

As is well known, in bright chromium plating techniques, the usual practice is to deposit a thin film of chromium on an electrolytically-deposited undercoating of another meta-l, conveniently nickel. As an alternative which affords many technical advantages, the use of an alloy containing copper and tin as the main constituents in place of nickel has much to recommend it, and various methods have been proposed in order to obtain a satisfac tory depositing under production conditions which involves certain difliculties. One method which largely overcomes these difiiculties is disclosed in our copending application Serial No. 320,617 filed November 14, 1952, now Patent No. 2,722,508.

All methods hitherto proposed for electrodepositing copper-tin alloy suitable as undercoating for bright chromium plate have, however, given a dull deposit which requires polishing or other brightening treatment if the subsequent chromium plating is to come out bright.

The major object of the present invention is to provide a method whereby copper-tin alloys may be deposited in a bright condition so that a subsequent bright chromium plating operation is possible without any intermediate treatment of the articles.

This improvement is of very considerable commercial importance as it makes it possible to transfer the articles being plated direct from the alloy plating bath to the bright chromium bath without the necessity of removing them from the plating jigs or suspenders in order to carry out a polishing or brightening treatment. Such intermediate treatment would usually involve unwiring the articles and hence an appreciable amount of labor, and the possibility of dispensing with it owing to the depositing of a bright alloy undercoating, represents therefore an important economic advantage.

According to the invention, the alloy coating may be obtained in the bright state by adopting a suitable chemical measure.

The chemical measures employed comprise the addition to the electrolyte of certain compounds of lead. The effect may be increased by the use of a secondary brightener which may consist of organic compounds such as acetates, cyanates, thiocyanates, tartrates, and/or citrates which may be supplied in the form of their alkali-metal salts or as salts of lead previously referred to.

An example of a suitable composition for the electrolyte is as follows:

EXAMPLE 1 Gm./l. Copper cyan 40 Sodium ctannate 20 Sodium cyanide (total) 65 Sodium hydroxide 7% Sodium citrate This gives a rather weak electrolyte and in circumstances in which the use of a more concentrated electrolyte is preferable, the following composition might be used:

The quantitiesof the various components may vary within the ranges defined by the upper and lower limits set forth in the two preceding examples.

For instance, the proportions by weight of the solids may vary as follows:

Percent Copper cyanide 5-25 Sodium stannate 10-50 Sodium cyanide 10-35 Sodium hydroxide 3- 5 Sodium citr 10-45 Other suitable examples of electrolyte compositions are as follows:

EXAMPLE 3 Preferred Concentra- Ooncentra- Percentage tion tion, g./l. Range Range,

g. ll.

copper carbonate- 7-60 20-80 potassium stannate 30 3-75 10-50 sodium cyanide (total) 7-60 20-80 sodium hydroxide 5 0. 25-20 1-20 potassium citrate 3-70 25-125 EXAMPLE 4 copper oxide 15 3-50 10-50 sodium stannate 100 3-50 10-50 potassium cyanide (total) 45 8-70 20-100 ammonium citrate 100 10-80 25-125 EXAMPLE 5 copper sulphite 50 7-50 20-80 sodium cyanide (total)c 50 7-50 20-80 sodium stannate 60 3-40 10-50 potassium hydroxide 60 10-40 20-100 citric acid 50 10-40 20-100 The various components may be added to the aqueous bath separately or they may be mixed in suitable proportions beforehand and subsequently dissolved in the appropriate amount of water.

The composition of the anodes, which primarily controls the nature of the deposit, may be -95% copper and 5-20% tin and very good results have been obtained with copper and 10% tin. It has also been found advantageous to include a small proportion gf aluminum or aluminum alloy, for instance, up to 2.5% of aluminum or up to 3% of an alloy of aluminum and magnesium.

The citrate or citric acid given in each of the above examples of electrolytes are not essential to the present invention.

According to the present "invention, there is added to an electrolyte-as setforthin the above-examples (with or without the citrate or citric acid present) a primary brightener compound of lead. Such compounds may include oxides, carbonates, cyanidesftar'trates or acetates.

It has been found that lead is the most eflective metal, the compounds ofwhich will serve as a primary brightener. Titanium, "which is also a metal of the fourth group or "the'Piio'di'c Table, does not satisfy therequirements or the present invention which are so well served by lead. x

The quantity of-t't he primary brighteher added to an electrolyte -'s'olu'tio'n containing the composition or any one or Examples -lwill vary from .01 to 1 gram per liter or about .003.3% of asoluble lead compound selected from the group'co'iisisti'ng of oxides and salts. It is preferred to add the brightener compound to the electrolyte-solution after-formation of the solution'rather than incorporating-it-wit-h the compositions of Examples 1-5 and adding theentire composition to the water. In other -words,-it-is-deemed advisable to add the brightener compound to theelectroly-te solution separately. Alternatively, the brightener may be included in the form of a small proportion of the appropriate metal alloyed with the anode.

The invention accordingly represents an important step forward in the plating art whereby improved results may be obtained with less labor.

We claim:

1. A process for the electrodeposition in bright form of alloys consisting mainly of copper and tin on a cathode comprising passing an electric current through an electrolytecontaining major portions of copper and tin, a primary brightener comprising about .003 to 3% of soluble compounds of lead selected from the group consisting of oxides and salts, and in which the cathode and an anode of the alloy to be deposited are immersed.

2. A process as claimed in claim 1 in which the effect of the primary brightener is increased by the addition to the electrolyte of a secondary brightener consisting of a metallic salt of an organic acid selected from the group consisting of acetic, cyanic, thiocyanic, tartaric and citric acids.

3. A process as claimed in claim 2 in which an organic salt of lead serves as both a primary and a secondary brightener.

4. A composition adapted for use when dissolved in water as the electrolyte in an electrolytic bath for the electrodeposition in bright form of an alloy consisting mainly of copper and tin, said composition comprising 525%'cop'pe1"cyanide, l'050% sodium stannate, l'0 35% sodium cyanide, 35% sodium hydroxide and .003 .3% of asolublelead compound selectedfrom the group consisting of oxides and salts.

5. A liquid for use as the electrolyte in -an'electrolytic bath for the electrodeposition in bright form of an alloy consisting mainly of copper and tin, said liquid comprising an aqueous solution containing dissolved solids in the proportion by weight of 545% copper cyanide, l0 sodium stannate, 10-35% sodium cyanide, 35% sodium hydroxide and .003.3% of a soluble lead compound selected from the group consisting of oxides and salts.

6. -A process =for theelectrodeposition in bright form of alloys consisting mainly of copper and tin on a cathode comprising passing an electric current through an electrolyte comprising an aqueous solution containing dissolved solids in the proportion by weight of 5 25% copper cyanide, lO50% sodium stannate, 10-35% sodium cyanide, *35% sodium hydroxide, and .0O3.3% of a soluble lead compound selected from the group consisting of oxides and salts and in which the cathode and an anode of the alloy to be deposited are immersed.

References Cited in the file of this patent UNITED STATES PATENTS 2,397,522 Baie'r Apr. 2, 1946 2,734,024 Schultz Feb. 7, 1956 FOREIGN PATENTS 679,947 Great Britain Sept. 24, 1952 OTHER REFERENCES Ser. No. 331,456, Weiner (A. P.'C.), published July 13, 1943. 

1. A PROCESS FOR THE ELETRODEPOSITION IN BRAIGHT FORM OF ALLOYS CONSISTING MAINLY OF COPPER AND TIN ON A CATHODE COMPRISING PASSING AN ELECTRIC CURRENT THROUGH AN ELECTROLYATE CONTAINING MAJOR PORTIONS OF COPPER AND TIN, A PRIMARY BRIGHTENER COMPRISING ABOUT .003 TO .3% OF SOLUBLE COMPOUNDS OF LEAD SELECTED FROM THE GROUP CONSISTING OF OXIDES AND SALTS, AND IN WHICH THE CATHODE AND AN ANODE OF THE ALLOY TO BE DEPOSITED ARE IMMERSED. 